Capture and Handling Stress Suppresses Circulating Levels of Thyroxine (T4) and Triiodothyronine (T3) in Beluga Whales Delphinapterus leucas

Twenty-four juvenile beluga whales, Delphinapterus leucas, were captured in western Hudson Bay. Seventeen were blood sampled and released immediately, one was held in shallow water for 15 h before release, and six were retained in captivity for 10 wk. Plasma concentrations of triiodothyronine (T3) decreased markedly during the first 24 h after capture, and by 2-4 days there was a similar reduction in thyroxine (T4). Concentrations of both hormones remained suppressed throughout the 10-wk period in captivity. Stimulation of adrenal activity by injection ofadrenocorticotropic hormone (ACTH) resulted in a further decline in T3 after 6-12 h. Handling stress was alone sufficient to produce similar changes in whales injected with saline as a control. This study demonstrated the acute sensitivity of thyroid hormone balance to stress in beluga whales.